1. Field of the Invention
The present invention relates generally to a CTD (charge transfer device) delay circuit and is directed more particularly to a CTD delay circuit suitable for use with a sterophonic sound extending circuit.
2. Description of the Prior Art
As shown in FIG. 1, a conventional stereophonic sound extending circuit, which emphasizes the separation of a stereophonic sound field, is formed of a matrix circuit 40 and a delay circuit or delay line 20.
Left and right channels, respectively, are provided between a left signal input terminal L.sub.Input and the matrix circuit 40 and between a right signal input terminal R.sub.Input and the matrix circuit 40. The delay line 20 is included in one or the other of the input channels (here shown in the left channel).
A left signal L, appearing at terminal L.sub.Input and provided to the delay line 20, is delayed and supplied as a delayed left signal L' to the matrix circuit 40. A right signal R appearing at the right signal input terminal R.sub.Input, is also applied to the matrix circuit 40, and the latter forms a composite signal L'-.DELTA.R by combining the left signal L' and a right stereo-enhancing signal-.DELTA.R which is proportional to the right signal R but is phase-inverted therefrom by 180.degree. and delivers the composite signal L'-.DELTA.R at one output terminal to an amplifier 51 which amplifies and supplies the composite signal to a left speaker 61. Similary, the right signal R from the input terminal R.sub.Input and a version of the phase-inverted delayed left signal .DELTA.L' are combined in the matrix circuit 40 to form another composite signal R-.DELTA.L' which is then supplied to an amplifier 52, where it is amplified and then fed to a right speaker 62.
When the signals applied to the input terminals L.sub.Input and R.sub.Input are stereophonic signals, the amount of stereophonic realism can be enhanced by increasing the amplitude of the phase inverted stereo-enhancing components .DELTA.R and .DELTA.L, the stereophonic sense can be emphasized. Such a technique is disclosed in U.S. Pat. No. 3,249,696, issued May 3, 1966 to Robert S. Van Sickle.
It is also known to apply a technique known as "delay stereophony" to make the sound on one channel seem deeper, or farther away, than the sound on the other channel. Thus, if monaural audio signals are applied to the input terminals L.sub.Input and R.sub.Input, the delay imparted by delay 20 to the signal on the left channel will bring about a quasi-stereophonic effect wherein the three-dimensional presence of the sound is improved.